From mboxrd@z Thu Jan 1 00:00:00 1970 From: Glauber de Oliveira Costa Subject: Re: [PATCH] raise tsc clocksource rating Date: Tue, 30 Oct 2007 10:02:18 -0200 Message-ID: <47271D4A.8030707@redhat.com> References: <11936994092607-git-send-email-gcosta@redhat.com> <1193697734.9793.86.camel@bodhitayantram.eng.vmware.com> <20071029224852.GA27547@elte.hu> <1193698505.9793.90.camel@bodhitayantram.eng.vmware.com> <20071029230213.GA1982@elte.hu> <1193699638.9793.97.camel@bodhitayantram.eng.vmware.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: jeremy-TSDbQ3PG+2Y@public.gmane.org, avi-i/T1Zxg06OZWk0Htik3J/w@public.gmane.org, kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, Dan Hecht , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Glauber de Oliveira Costa , --cc-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, Garrett Smith To: Zachary Amsden Return-path: In-Reply-To: <1193699638.9793.97.camel-cxY/u30q8FloTgUnLF1by8fTvwmfpRNyZeezCHUQhQ4@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Zachary Amsden escreveu: > On Tue, 2007-10-30 at 00:02 +0100, Ingo Molnar wrote: >> * Zachary Amsden wrote: > >>> Not every guest support paravirt, but for correctness, all guests >>> require TSC, which must be exposed all the way up to userspace, no >>> matter what the efficiency or accuracy may be. >> but if there's a perfect TSC available (there is such hardware) then the >> TSC _is_ the best clocksource. Paravirt now turns it off unconditionally >> in essence. > > No, if no paravirt clocksource is detected, nothing can override the > perfect TSC hardware clocksource rating of 400. And if a paravirt > clocksource is detected, it is always better than TSC. Why always? tsc is the best possible alternative the _platform_ can provide. So the paravirt clocksource will be at best, as good as tsc. And if it is the case: why bother with communication mechanisms of all kinds, calculations, etc, if we can just read the tsc? Noting again: If the tsc does not arrive accurate to the guest, it will fail the tsc clocksource tests. So it will be rated zero anyway -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.7 (GNU/Linux) Comment: Using GnuPG with Remi - http://enigmail.mozdev.org iD8DBQFHJx1KjYI8LaFUWXMRAv0hAJ4sj0Z1FraYrgbU5Mj0pWOJGk6jtwCfc5xL jpTC273X0oqPTCR7NcVHJOI= =WPzV -----END PGP SIGNATURE----- ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/